/**
 * \file time.c
 * \author Radek Krejci <rkrejci@cesnet.cz>
 * \brief libnetconf2 - time handling functions
 *
 * Copyright (c) 2015 CESNET, z.s.p.o.
 *
 * This source code is licensed under BSD 3-Clause License (the "License").
 * You may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://opensource.org/licenses/BSD-3-Clause
 */

#define _GNU_SOURCE
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "libnetconf.h"

API time_t
nc_datetime2time(const char *datetime)
{
    struct tm time;
    char *dt;
    int i;
    long int shift, shift_m;
    time_t retval;

    if (!datetime) {
        ERRARG("datetime");
        return -1;
    }

    dt = strdup(datetime);
    if (!dt) {
        ERRMEM;
        return -1;
    }

    if (strlen(dt) < 20 || dt[4] != '-' || dt[7] != '-' || dt[13] != ':' || dt[16] != ':') {
        ERR("Wrong date time format not compliant to RFC 3339.");
        free(dt);
        return (-1);
    }

    memset(&time, 0, sizeof(struct tm));
    time.tm_year = atoi(&dt[0]) - 1900;
    time.tm_mon = atoi(&dt[5]) - 1;
    time.tm_mday = atoi(&dt[8]);
    time.tm_hour = atoi(&dt[11]);
    time.tm_min = atoi(&dt[14]);
    time.tm_sec = atoi(&dt[17]);

    retval = timegm(&time);

    /* apply offset */
    i = 19;
    if (dt[i] == '.') { /* we have fractions to skip */
        for (i++; isdigit(dt[i]); i++)
            ;
    }
    if (dt[i] == 'Z' || dt[i] == 'z') {
        /* zero shift */
        shift = 0;
    } else if (dt[i + 3] != ':') {
        /* wrong format */
        ERR("Wrong date time shift format not compliant to RFC 3339.");
        free(dt);
        return (-1);
    } else {
        shift = strtol(&dt[i], NULL, 10);
        shift = shift * 60 * 60; /* convert from hours to seconds */
        shift_m = strtol(&dt[i + 4], NULL, 10) * 60; /* includes conversion from minutes to seconds */
        /* correct sign */
        if (shift < 0) {
            shift_m *= -1;
        }
        /* connect hours and minutes of the shift */
        shift = shift + shift_m;
    }
    /* we have to shift to the opposite way to correct the time */
    retval -= shift;

    free(dt);
    return retval;
}

API char *
nc_time2datetime(time_t time, const char *tz, char *buf)
{
    char *date = NULL;
    char *zoneshift = NULL;
    int zonediff, zonediff_h, zonediff_m;
    struct tm tm, *tm_ret;
    char *tz_origin;

    if (tz) {
        tz_origin = getenv("TZ");
        if (tz_origin) {
            tz_origin = strdup(tz_origin);
            if (!tz_origin) {
                ERRMEM;
                return NULL;
            }
        }
        setenv("TZ", tz, 1);
        tzset(); /* apply timezone change */
        tm_ret = localtime_r(&time, &tm);
        if (tz_origin) {
            setenv("TZ", tz_origin, 1);
            free(tz_origin);
        } else {
            unsetenv("TZ");
        }
        tzset(); /* apply timezone change */

        if (!tm_ret) {
            return NULL;
        }
    } else {
        if (!gmtime_r(&time, &tm)) {
            return NULL;
        }
    }

    /* years cannot be negative */
    if (tm.tm_year < -1900) {
        ERRARG("time");
        return NULL;
    }

    if (tm.tm_gmtoff == 0) {
        /* time is Zulu (UTC) */
        if (asprintf(&zoneshift, "Z") == -1) {
            ERRMEM;
            return NULL;
        }
    } else {
        zonediff = tm.tm_gmtoff;
        zonediff_h = zonediff / 60 / 60;
        zonediff_m = zonediff / 60 % 60;
        if (asprintf(&zoneshift, "%+03d:%02d", zonediff_h, zonediff_m) == -1) {
            ERRMEM;
            return NULL;
        }
    }

    if (buf) {
        sprintf(buf, "%04d-%02d-%02dT%02d:%02d:%02d%s",
                        tm.tm_year + 1900,
                        tm.tm_mon + 1,
                        tm.tm_mday,
                        tm.tm_hour,
                        tm.tm_min,
                        tm.tm_sec,
                        zoneshift);
    } else if (asprintf(&date, "%04d-%02d-%02dT%02d:%02d:%02d%s",
                        tm.tm_year + 1900,
                        tm.tm_mon + 1,
                        tm.tm_mday,
                        tm.tm_hour,
                        tm.tm_min,
                        tm.tm_sec,
                        zoneshift) == -1) {
        free(zoneshift);
        ERRMEM;
        return NULL;
    }
    free(zoneshift);

    return (buf ? buf : date);
}